U.S. patent application number 11/490527 was filed with the patent office on 2007-01-25 for image forming apparatus.
Invention is credited to Hideki Ishida, Hirohito Kondo, Eiji Tatsumi.
Application Number | 20070019057 11/490527 |
Document ID | / |
Family ID | 32512127 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070019057 |
Kind Code |
A1 |
Kondo; Hirohito ; et
al. |
January 25, 2007 |
Image forming apparatus
Abstract
Such an image forming device is supplied as can prevent uneven
density of images and enhance image quality, including an LED array
control unit that controls driving of an LED print head and a
selective-information-data feeding unit that feeds information data
corresponding information selected from inherent selective
information. The control unit is provided with a
characteristic-data memory unit that memorizes a plurality of
characteristic data concerning each of LED elements forming the LED
array, a driving-current-correction-data calculation unit, an
image-signals processing unit and an image-data correction
calculation unit. The current-correction-data calculation unit
reads out characteristic data from the characteristic-data memory
unit, receives selected information data from the data feeding unit
and calculates driving current correction data based on these data.
The image-data correction calculation unit corrects image data fed
from the signals processing unit by using current correction data
and feeds the corrected image data to the print head.
Inventors: |
Kondo; Hirohito; (Osaka-shi,
JP) ; Ishida; Hideki; (Osaka-shi, JP) ;
Tatsumi; Eiji; (Osaka-shi, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
Suite 800
1850 M Street, N.W.
Washington
DC
20036
US
|
Family ID: |
32512127 |
Appl. No.: |
11/490527 |
Filed: |
July 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10731010 |
Dec 10, 2003 |
|
|
|
11490527 |
Jul 21, 2006 |
|
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Current U.S.
Class: |
347/130 |
Current CPC
Class: |
G06K 15/1247
20130101 |
Class at
Publication: |
347/130 |
International
Class: |
B41J 2/385 20060101
B41J002/385 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2002 |
JP |
2002-360640 |
Dec 12, 2002 |
JP |
2002-360661 |
Dec 12, 2002 |
JP |
2002-360673 |
Claims
1-11. (canceled)
12. An image forming apparatus comprising: an LED print head
comprising an LED array including a plurality of LED elements whose
lighting is controlled according to image data and a driving
circuit for driving the of LED elements; and an LED array
controller for controlling driving of the LED print head, wherein
the image forming apparatus further comprises: a paper image data
feeder for reading an image formed by the image forming apparatus
on a sheet of paper output therefrom in order to feed out paper
image data representing a degree of density unevenness of the
image, and wherein the LED array controller comprises: a
characteristic data memory for storing a plurality of sets of
characteristic data each relating to one of the plurality of LED
elements; and a driving current correction data calculator for
reading out the characteristic data from the characteristic data
memory while receiving the paper image data from the paper image
data feeder in order to calculate, based on the characteristic
data, driving current correction data for each of the plurality of
LED elements and increase or decrease the driving current
correction data according to the paper image data.
13. An image forming apparatus as claimed in claim 12, wherein the
paper image data feeder includes an image sensor for reading the
image formed on the sheet of paper output from the image forming
apparatus.
14. An image forming apparatus comprising: an LED print head
including an LED array composed of a plurality of LED elements
whose lighting is controlled according to image data and a driving
circuit for driving the LED elements; and an LED array controller
for controlling driving of the LED print head, wherein the image
forming apparatus further comprises a toner image data feeder for
reading a toner image formed on an image-carrying member by the
image forming apparatus in order to feed out toner image data
representing a degree of density unevenness of the image, and
wherein the LED array controller comprises: a characteristic data
memory for storing a plurality of sets of characteristic data each
relating to one of the plurality of LED elements; and a driving
current correction data calculator for reading out the
characteristic data from the characteristic data memory while
receiving the toner image data from the toner image data feeder in
order to calculate, based on the characteristic data, driving
current correction data for each of the plurality of LED elements
and increase or decrease the driving current correction data
according to the toner image data.
15. An image forming apparatus as claimed in claim 14, wherein the
image-carrying member is a photoconductor or a transport belt.
16. An image forming apparatus as claimed in claim 14, wherein the
toner data feeder includes an image sensor for reading the toner
image formed on the image-carrying member.
17. An image forming apparatus as claimed in claim 12, wherein the
LED array controller further comprises a driving current correction
data memory for reading out the driving current correction data
calculated and increased or decreased by the driving current
correction data calculator and for storing the driving current
correction data thus read out.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image forming apparatus
employing an LED (Light Emitting Diode) print head as an exposing
measure, such as an electro-photographic printer, a facsimile
apparatus, a copier and the like.
[0003] 2. Description of the Prior Art
[0004] In recent years, an electro-photographic image forming
apparatus employing an LED array as a measure for recording an
image by exposure has been attracted attention, in order to
miniaturize and simplify the apparatus. In this
electro-photographic image forming apparatus, an LED print head
used for exposure of a photoreceptor includes an LED array which is
formed by placing a plurality of LED elements in a line, and
thereby can choose the LED elements so as to make them emit light
individually, based on image data.
[0005] However, it is impossible to manufacture a plurality of LED
elements that forms the LED array in such a manner that
light-emitting characteristic thereof is uniform. Therefore,
although the same amount of electric current is applied to all the
LED elements, light quantity thereof differs, depending on each of
the LED elements, thereby causing variations in light quantity
among the LED elements. As a result, image density becomes
uneven.
[0006] Therefore, such LED print heads are proposed as, wherein,
correction is made in order to make the light quantity of the LED
elements uniform. For example, the following LED print heads are
proposed, wherein: for the purpose of standardizing light-emitting
output of an LED printer and enhancing printing quality thereof,
electric current to be supplied to each of the LED elements is
controlled and the light quantity thereof is made uniform, by
trimming with laser beam so as to adjust a resistance value. (For
example, see Japanese Laid-Open Patent Application No. H5-4376
(pages 3 and 4, FIGS. 6 through 8.)) Moreover, another example is
proposed, wherein: for the purpose of requiring no adjustment in
installing an LED print head having variations in light quantity or
requiring no adjustment in replacing the LED print head, correction
data that make light-emitting amount of the LED elements uniform
are obtained in advance; an ROM saving the relevant correction data
in the LED print head is provided; and each of the LED elements is
lighted at the time of printing by using the correction data. (For
example, see Japanese Laid-Open Patent Application No. H5-50653
(pages 4 and 4, FIG. 1).)
[0007] However, since light image data emitted from the LED
elements are formed into a latent image on a photoreceptor through
a lens array, the image forming apparatuses including the above
conventional LED print heads have the diameter of dots formed
therein differ according to each of the LED elements, due to
variation in optical characteristics of the lens array and the
like, although the light quantity of the LED elements is made
uniform. Therefore, it has been impossible to standardize
distribution of the light quantity, thereby causing an
inconvenience that vertical streaks occur on images. For example,
as shown in FIG. 10, although the light quantities of both LED
elements of an LED element a' and an LED element b' are the same,
the dot diameters S.sub.a' and S.sub.b' of both LED elements in
development threshold values are different (S.sub.a'<S.sub.b').
Therefore, the LED element b' having a larger dot diameter in the
development threshold value has larger latent image dots and
thereby is expressed in dark in the image.
[0008] Moreover, image forming apparatuses are provided with
various screens used for special image processing, toners of
various colors used for color printing and the like, all of which
can be set optionally. However, screens, toners and the like that
are inherent to the image forming apparatuses have properties that
are different from each other. Therefore, simply making the light
quantity of the LED elements uniform will cause a difference in the
image quality among images, depending on each of the screens, toner
colors and the like.
[0009] Furthermore, in image forming apparatuses, properties of LED
elements, photoreceptors, toners and the like vary or get
deteriorated in accordance with a change due to ageing in
application environments such as temperature and humidity and in
accordance with a change due to ageing in the number of usage and
the like. As a result, light quantity of the LED elements,
electrostatic charging characteristic of photoreceptors or charging
characteristic of toners will change. In consequence, since the
image quality changes as time passes by, it is impossible to
overcome the change in the image quality due to aging simply by
standardizing the light quantity of the LED elements.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide an image
forming apparatus that can restrain uneven density of images and
improve image quality thereof.
[0011] To achieve the above object, according to one aspect of the
present invention, in an image forming apparatus provided with an
LED print head, which includes an LED array composed of a plurality
of LED elements whose lighting is controlled according to image
data and a driving circuit for driving the plurality of LED
elements, and an LED array controller for controlling driving of
the LED print head, the image forming apparatus is further provided
with a selective-information data feeder for storing information
data corresponding to different sets of selective information
inherent to the image forming apparatus and for feeding out
information data corresponding to a selected item of the selective
information, and the LED array controller is provided with a
characteristic data memory for storing a plurality of sets of
characteristic data each relating to one of the plurality of LED
elements and a driving current correction data calculator for
reading out the characteristic data from the characteristic data
memory while receiving the information data from the
selective-information data feeder in order to calculate, based on
the characteristic data and the information data, driving current
correction data for each of the plurality of LED elements.
[0012] Here, preferably, the different sets of selective
information correspond to a plurality of screens with different
characteristics, or correspond to a plurality of toner colors.
[0013] With this configuration, the driving current correction data
for the individual LED elements is calculated from the
characteristic data relating to the individual LED elements, which
causes uneven density in the produced image, and the information
data corresponding to a particular set of selective information,
which affects the image quality of the produced image, and the
individual LED elements are lit on the basis of the thus calculated
driving current correction data. This makes it possible to
accurately cancel differences in display density among the
individual LED elements constituting the LED array and thereby
obtain less uneven density in the produced image. Moreover, it is
possible to efficiently reduce the appearance of vertical streaks
in the produced image.
[0014] To achieve the above object, according to another aspect of
the present invention, in an image forming apparatus provided with
an LED print head, which includes an LED array composed of a
plurality of LED elements whose lighting is controlled according to
image data and a drive circuit for driving the plurality of LED
elements, and an LED array controller for controlling driving of
the LED print head, the image forming apparatus is further provided
with a detected data feeder for detecting time-related variation in
the image forming apparatus in order to feed out detected data, and
the LED array controller is provided with a characteristic data
memory for storing a plurality of sets of characteristic data each
relating to one of the plurality of LED elements and a drive
current correction data calculator for reading out the
characteristic data from the characteristic data memory while
receiving the detected data from the detected data feeder in order
to calculate, based on the characteristic data, drive current
correction data for each of the plurality of LED elements and
increase or decrease the drive current correction data according to
the detected data.
[0015] Here, preferably, the detected data feeder detects the
atmospheric temperature or humidity inside the image forming
apparatus and feeds out the temperature or humidity as the detected
data, or detects the number of sheets of paper on which the image
forming apparatus has formed an image and feeds out the number as
the detected data. Alternatively, the detected data feeder may
detect the developing bias potential or the dark and light
potentials in the image forming apparatus and feed out the
developing bias voltage or the dark and light potentials as the
detected data.
[0016] With this configuration, the driving current correction data
for the individual LED elements is calculated from the
characteristic data relating to the individual LED elements, which
causes uneven density in the produced image, and the thus
calculated driving current correction data is increased or
decreased according to detected data of time-related variations
that affect the time-related variation of the quality of the
produced image so that the individual LED elements are lit on the
basis of the thus increased or decreased driving current correction
data. This makes it possible to accurately cancel differences in
display density among the individual LED elements constituting the
LED array and thereby obtain less uneven density in the produced
image. Moreover, it is possible to efficiently reduce the
appearance of vertical streaks in the produced image.
[0017] To achieve the above object, according to another aspect of
the present invention, in an image forming apparatus provided with
an LED print head, which includes an LED array composed of a
plurality of LED elements whose lighting is controlled according to
image data and a drive circuit for driving the plurality of LED
elements, and an LED array controller for controlling driving of
the LED print head, the image forming apparatus is further provided
with a paper image data feeder for reading an image formed by the
image forming apparatus on a sheet of paper output therefrom in
order to feed out paper image data, and the LED array controller is
provided with a characteristic data memory for storing a plurality
of sets of characteristic data each relating to one of the
plurality of LED elements and a drive current correction data
calculator for reading out the characteristic data from the
characteristic data memory while receiving the paper image data
from the paper image data feeder in order to calculate, based on
the characteristic data, drive current correction data for each of
the plurality of LED elements and increase or decrease the drive
current correction data according to the paper image data.
[0018] Here, preferably, the paper image data feeder includes an
image sensor for reading the image formed on the sheet of paper
output from the image forming apparatus.
[0019] Alternatively, in an image forming apparatus provided with
an LED print head, which includes an LED array composed of a
plurality of LED elements whose lighting is controlled according to
image data and a drive circuit for driving the plurality of LED
elements, and an LED array controller for controlling driving of
the LED print head, wherein the image forming apparatus is further
provided with a toner image data feeder for reading a toner image
formed on an image-carrying member by the image forming apparatus
in order to feed out toner image data, and the LED array controller
is provided with a characteristic data memory for storing a
plurality of sets of characteristic data each relating to one of
the plurality of LED elements and a drive current correction data
calculator for reading out the characteristic data from the
characteristic data memory while receiving the toner image data
from the toner image data feeder in order to calculate, based on
the characteristic data, drive current correction data for each of
the plurality of LED elements and increase or decrease the drive
current correction data according to the toner image data.
[0020] Here, preferably, the image-carrying member is a
photoconductor or a transport belt. Moreover, preferably, the toner
data feeder includes an image sensor for reading the toner image
formed on the image-carrying member.
[0021] With this configuration, the driving current correction data
for the individual LED elements is calculated from the
characteristic data relating to the individual LED elements, which
causes uneven density in the produced image, and the thus
calculated driving current correction data is increased or
decreased according to the paper image data or toner image data
that is reflected in the time-related variation of the quality of
the produced image so that the individual LED elements are lit on
the basis of the thus increased or decreased driving current
correction data. This makes it possible to accurately cancel
differences in display density among the individual LED elements
constituting the LED array and thereby obtain less uneven density
in the produced image. Moreover, it is possible to efficiently
reduce the appearance of vertical streaks in the produced
image.
[0022] Preferably, the LED array controller is further provided
with a drive current correction data memory for reading out the
drive current correction data calculated and increased or decreased
by the drive current correction data calculator and for storing the
drive current correction data thus read out. The reason is that,
even when it takes a long time for the driving current correction
data calculator to calculate the driving current correction data,
if previously calculated driving current correction data is stored
in the driving current correction data memory, it is possible to
correct the image data more quickly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] This and other objects and features of the present invention
will become clear from the following description, taken in
conjunction with the preferred embodiments with reference to the
accompanying drawings in which:
[0024] FIG. 1 is a simplified schematic diagram showing the entire
construction of an image forming apparatus common to embodiments of
the present invention;
[0025] FIG. 2 is a schematic view showing a simplified construction
of an LED array exposure device in an image forming apparatus
common to embodiments of the present invention;
[0026] FIG. 3 is a schematic view showing an LED array exposure
device installed to an image forming apparatus;
[0027] FIG. 4 is a block diagram showing the construction of an LED
array control unit in an image forming apparatus according to a
first embodiment of the present invention;
[0028] FIG. 5 is a block diagram showing the construction of a
driving circuit of an LED print head of an image forming apparatus
common to the embodiments of the present invention;
[0029] FIG. 6 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the first embodiment;
[0030] FIG. 7 is a block diagram showing the construction of an LED
array control unit in an image forming apparatus according to a
second embodiment of the present invention;
[0031] FIG. 8 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the second embodiment;
[0032] FIG. 9 is a block diagram showing the construction of an LED
array control unit in an image forming apparatus according to a
third embodiment of the present invention;
[0033] FIG. 10 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the third embodiment;
[0034] FIG. 11 is a block diagram showing the construction of an
LED array control unit in an image forming apparatus according to a
fourth embodiment of the present invention;
[0035] FIG. 12 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the fourth embodiment;
[0036] FIG. 13 is a block diagram showing the construction of an
LED array control unit in an image forming apparatus according to a
fifth embodiment of the present invention;
[0037] FIG. 14 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the fifth embodiment;
[0038] FIG. 15 is a block diagram showing the construction of an
LED array control unit in an image forming apparatus according to a
sixth embodiment of the present invention;
[0039] FIG. 16 is a flow chart showing a procedure for lighting
control of LED elements of the image forming apparatus according to
the sixth embodiment;
[0040] FIG. 17 is a block diagram showing the construction of an
LED array control unit in an image forming apparatus according to a
seventh embodiment of the present invention;
[0041] FIG. 18 is a block diagram showing the construction of an
LED array control unit in an image forming apparatus according to
an eighth embodiment of the present invention;
[0042] FIGS. 19A and 19B are diagrams showing the relationship
between the exposure intensity and the beam diameter in development
threshold value of LED elements of the image forming apparatus
according to the embodiments of the present invention; and
[0043] FIG. 20 is a diagram showing the relationship between the
contrast of density and the beam diameter in the development
threshold value of the LED elements of the conventional image
forming apparatuses.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Hereinafter, embodiments of the present invention will be
described with reference to the drawings. FIG. 1 is a simplified
schematic diagram showing the entire construction of an image
forming apparatus common to embodiments of the present invention.
In an image forming apparatus shown in FIG. 1, reference numeral 1
represents a color printer as an example of an image forming
apparatus. The color printer 1 comprises a housing 2, an image
forming unit for black 3B, an image forming unit for yellow 3Y, an
image forming unit for cyan 3C, an image forming unit for magenta
3M, toner hoppers 10B, 10Y, 10C and 10M respectively for each of
the aforementioned colors, a paper feed cassette 12 for storing a
plurality of papers 14, a paper feed guide 13, transport belt
driving rollers 11a and 11b, a transport belt 8, image transfer
rollers 9, a fusing unit 17, a paper feed-out guide 15, and a paper
feed-out area 16. In addition, each of the image forming units 3B,
3Y, 3C and 3M for each color comprises a developing unit 4, a
photoreceptor 5 as an image-carrying substance, a main charging
unit 6, an LED print head 7, and a cleaning unit 20.
[0045] In the color printer 1, an electrostatic latent image is
formed by the LED print head 7 on the photoreceptor 5 that has been
charged by the main charging unit 6. Then, a toner image is
developed by the developing unit 4 so that a visible image is
formed. This process is performed for each of the above colors of
black, yellow, cyan and magenta. The paper 14 fed from the paper
feed cassette 12 is guided through the paper feed guide 13 and
absorbed onto an upper face of the transport belt 8 which is
rotating in a counterclockwise direction, and when the paper 14
passes right under each of the image forming units 3B, 3Y, 3C and
3M for each color, a toner image in each color is transferred onto
the paper 14 one after another by the transfer roller 9. Toners in
four colors forming a full-color image on the paper 14 in this way
are fused when the paper 14 passes through the fusing unit 17.
After that, the paper 14 is fed out into the paper feed-out area
16, guided by the paper feed-out guide 15.
[0046] Next, the LED print head 7 installed to the above-mentioned
color printer 1 is described with reference to FIG. 2. FIG. 2 is a
schematic diagram showing a simplified construction of an LED array
print head in an image forming apparatus common to the embodiments
of the present invention. In FIG. 2, the LED print head 7 comprises
a LED array including a plurality of LED's laid in line on a
substrate 30 having wiring and controlled in lighting in accordance
with image data, a lens array 32 arranged over the LED array 31 so
as to form a full-size erect image, and a driving circuit 33 that
drives a plurality of LED elements forming the LED array 31. Here,
the substrate 30, the lens array 32 and the like are supported by
unillustrated structural members. Additionally, an LED array
control unit 34 controlling the driving of the LED print head 7 is
provided externally.
[0047] FIG. 3 is a schematic view showing the LED print head 7
installed into an image forming apparatus. In FIG. 3, reference
numeral 5 represents a photoreceptor having a shape of a drum. Also
in the diagram, shown in broken line is how the lens array 32
receives and refracts the light emitted from LED elements so as to
form an image on a surface of the drum.
[0048] As described above, each LED element is driven in accordance
with image signals transmitted to the color printer 1 in FIG. 1
from an unillustrated external PC and the like and emits light. The
light emitted from the LED elements forms an image as a dot on a
surface of the photoreceptor 5 through the lens array 32. The image
forming apparatus of the present invention is so formed as to have
pixels owning larger exposure energy (or light-emitting energy of
LED elements) on the photoreceptor 5 have higher density. This
exposure energy (or the light-emitting energy of the LED elements)
is represented by a formula: exposure intensity of the LED
elements(=driving current).times.lighting time(=time for supply of
driving current).
[0049] Next, by referring to FIGS. 4 and 5, performance of the LED
array control unit and performance of the driving circuit of the
LED print head will be described. FIG. 4 is a block diagram showing
the construction of an LED array control unit of the image forming
apparatus according to a first embodiment of the present invention.
FIG. 5 is a block diagram showing the construction of a driving
circuit of an LED print head in the image forming apparatus common
to the embodiments of the present invention.
[0050] The LED array control unit 34 controls driving of the LED
print head 7, comprising a characteristic-data memory unit 35, a
driving-current-correction-data calculation unit 39, a
image-signals processing unit 43, a control-signals generating unit
43 and an image-data correction calculation unit 44. Additionally,
the LED array control unit 34 has a selective-information-data
feeding unit 60 provided externally.
[0051] The image-signals processing unit 42 is a measure to perform
image processing such as tone processing and the like in an
appropriate manner for image signals 41 transmitted to the LED
array control unit 34 from external devices such as a frame memory,
a scanner and the like and to convert the image signals 41 into
image data. The image data are data which show the density of
pixels separated according to each of the aforementioned four
colors of black, yellow, cyan and magenta, and are m-bit digital
data showing driving current (light-emitting intensity) and
lighting time (time for supply of driving current) of the LED
elements. Image data processed by the image-signals processing unit
42 are fed to the image-data correction calculation unit 44.
[0052] The characteristic-data memory unit 35 is a measure to
memorize a plurality of pre-measured characteristic data concerning
each of a plurality of LED elements forming the LED array 31. For
example, as shown in FIG. 4, the characteristic-data memory unit 35
comprises a light-quantity-data memory unit 36 that memorizes data
on light quantity concerning each of the LED elements as
characteristic data; a beam-data memory unit 37 that memorizes data
concerning beams emitted from the LED elements, for example, data
concerning beam diameter and beam area, as characteristic data; and
a resolution-data memory unit 38 that memorizes data showing
resolution of each of the LED elements, for example, Modulation
Transfer Function (MTF) data, as characteristic data. The
characteristic-data memory unit 35, for example, includes a Read on
Memory (ROM), but may be so constructed as to include a
transferable PROM (e.g. EPROM that deletes data by using
ultraviolet rays or EEPROM that deletes data electrically) in order
to correspond to a change in properties of individual LED
elements.
[0053] The selective-information-data feeding unit 60 is provided
with a screen-information-data memory unit 61 storing information
data corresponding respectively to each of selective information on
a plurality of screens different from each other in properties and
selective information on a plurality of toner colors, that are
selective information inherent to the image forming apparatus of
the present invention, and is provided with a
toner-color-information-data memory unit 62; extracts information
data corresponding to selective information on screens and toners,
which are selected by inputting from an unillustrated operation
unit, from the screen-information-data memory unit 61 and the
toner-color-information-data memory unit 62; and feeds to the
driving-current-correction-data calculation unit 39, which will be
described hereinafter in details. Representative plurality of toner
colors are black, yellow, cyan and magenta.
[0054] Next, the driving-current-correction-data calculation unit
39 is connected to the characteristic-data memory unit 35 and the
selective-information-data feeding unit 60, read outs each of the
characteristic data memorized in the light-quantity-data memory
unit 36, the beam-data memory unit 37 and the resolution-data
memory unit 38, all of which are installed in the
characteristic-data memory unit 35; receives information data
corresponding to selective information on screens and toner colors
selected and fed from the selective-information-data feeding unit
60; and calculates driving current correction data P for each of a
plurality of LED elements forming the LED array 31 in accordance
with a predetermined calculation formula, based on the
characteristic data and the information data. The driving current
correction data P calculated by the driving-current-correction-data
calculation unit 39 are fed to the image-data correction
calculation unit 44.
[0055] As described later, the driving current correction data P
are data that are used when exposure intensity of each individual
LED element is changed by changing the driving current of each
individual of the individual LED elements forming the LED array 31.
For example, when the driving current of a dot #1 (a first LED
element) is corrected, driving current correction data P.sub.1 are
used; and when the driving current of a dot #n. (an n-th LED
element) is corrected, driving current correction data P.sub.n are
used.
[0056] The image-data correction calculation unit 44 corrects image
data fed by the image-signals processing unit 42 by using driving
current correction data P fed by the
driving-current-correction-data calculation unit 39. In other
words, the image-data correction calculation unit 44 corrects m-bit
digital data showing the driving current of each individual of the
LED elements forming the LED array 31, among the image data fed by
the image-signals processing unit 42, in accordance with the
driving current correction data P fed by the
driving-current-correction-data calculation unit 39. The image data
subjected to the relevant correction are fed to the LED print head
7, as shown in FIG. 4.
[0057] A driving circuit 33 of the LED print head 7, as shown in
FIG. 5, includes a CLK counter 50 that counts clock signals CLK, an
SCLK counter 51 that counts strobe clock signals SCLK, a saving
unit 52 that temporarily saves image data showing pixel densities
after correction, a gate unit 53 that opens and closes in
accordance with a logic of feeding time control signals STROBE, and
a constant-current generation unit 54 that generates driving
current of the LED array 31.
[0058] A driving circuit 33 of the LED print head 7 with the
construction as mentioned above initiates receiving post-correction
image data that are fed by being initialized by changing from high
level to low level of horizontal synchronization signals HSYNC fed
from the control-signals generation unit 43 and by synchronizing
with the clock signal CLK input from the control-signals generation
unit 43 and with the clock signal CLK.
[0059] The saving unit 52 is provided with a shift register and a
latch circuit, wherein data necessary for light-emission of the LED
array 31 are temporarily saved in order to convert image data fed
after correction. Here, driving methods of the LED elements forming
the LED print head include a static driving method that controls
lighting-on and lighting-off of all LED elements simultaneously,
and a dynamic driving method that divides the LED's into a
plurality of blocks and controls lighting-on and lighting-off of
each individual block thereof. In case of adopting the static
driving method, data for all the LED elements are saved
temporarily, while in case of adopting the dynamic driving method,
data for one block are saved temporarily.
[0060] The CLK counter 50 determines whether or not temporary
saving of image data in the saving unit 52 has been completed,
based on the number of counts of clock signals CLK, and when such
temporary saving is determined to have been completed, transmits a
light-emitting timing control signal STREQ to the control-signals
generating unit 43 so as to show that preparation is made for
emitting a light.
[0061] The control-signals generation unit 43 that receives a
light-emitting timing control signal STREQ sets a feeding time
control signal STROBE to be at the active level (low level), and
when strobe clock signals SCLK begin to be fed, the SCLK counter 51
starts counting the strobe clock signals SCLK and then the gate
unit 53 is released. As a result, the LED elements forming the LED
array 31 have driving current based on driving current correction
data P saved in the saving unit 52 flow thereon for a period as
long as light-emitting time based on the image data saved in the
saving unit 52, and consequently, the photoreceptor 5 is
exposed.
[0062] FIG. 6 is a flow chart showing a procedure for lighting
control of the LED elements according to the first embodiment. In
this control procedure, first of all, n=1 is set in order to make
the first line of the total number of lines N targeted. (Step S1)
Next, characteristic data of each of the LED elements are read out
from the characteristic-data memory unit 35, receiving information
data corresponding to selective information that is selected and
fed from the selective-information-data feeding unit 60 (Step S2);
and driving current correction data P for each of the LED elements
are calculated in the driving-current-correction-data calculation
unit 39. (Step S3) Then, calculated driving current correction data
P are fed to the image-data correction calculation unit 44 (Step
S4), and in the image-data correction calculation unit 44, image
data are corrected. (Step S5) Next, corrected image data are fed to
the LED print head (Step S6), and the LED elements are lighted in
accordance with the corrected image data. (Step S7) Then, in order
to have the next line "n" targeted, an increment of +1 is supplied
to the number "n" (Step S8), checking to ensure that the number "n"
does not exceed the total line number N to be printed. (Step S9)
When the number "n" does not exceed the total line number N, the
above processing will be repeated in the same manner for the line
"n." (Steps S2 through S9)
[0063] The first embodiment of the present invention is constructed
in such a manner as driving current correction data P are directly
fed to the image-data correction calculation unit 44 after
calculated by the driving-current-correction-data calculation unit
39. However, as shown in FIG. 7, it may be so constructed as to
have a driving-current-correction-data memory unit 40, which
memorizes driving current correction data P calculated in the
driving-current-correction-data calculation unit 39, provided
thereto separately and to have the driving-current-correction-data
memory unit 40 connected to the driving-current-correction-data
calculation unit 39 and the image-data correction calculation unit
44. This construction will be described hereinafter as a second
embodiment of the present invention.
[0064] According to the second embodiment of the present invention,
the driving-current-correction-data memory unit 40 reads out
driving current correction data P from the
driving-current-correction-data calculation unit 39, memorizes the
operating current correction data P and feeds the driving current
correction data P to the image-data correction calculation unit 44.
In order to cope with a change of the driving current correction
data P based on a change in characteristics and the like of each of
individual LED element, the driving-current-correction-data memory
unit 40 is provided with, for example, a transferable PROM (e.g.
EPROM that deletes data with ultraviolet rays or EEPROM that
deletes data electrically) and the like.
[0065] With the above-mentioned configuration, although calculation
of driving current correction data P takes a long time, it is
possible to read out driving current correction data P rapidly in
the image-data correction calculation unit 44 because
pre-calculated driving current correction data P are memorized in
the driving-current-correction-data memory unit 40. As a result, it
becomes possible for the image-data correction calculation unit 44
to correct image data rapidly.
[0066] A procedure for lighting control of the LED elements is
followed in accordance with the flow chart shown in FIG. 8. Namely,
first of all, n=1 is set in order to make the first line of the
total number of lines N targeted. (Step S100) Next, characteristic
data of each of the LED elements are read out from the
characteristic-data memory unit 35, receiving information data
corresponding to selective information that is selected and fed
from the selective-information-data feeding unit 60 (Step S101);
and driving current correction data P of each of the LED elements
are calculated in the driving-current-correction-data calculation
unit 39. (Step S102) Then, calculated driving current correction
data P are memorized in the driving-current-correction-data memory
unit 40. (Step S103) Next, in order to have the next line "n"
targeted, an increment of +1 is supplied to the number "n" (Step
S104), checking to ensure that the number "n" does not exceed the
total line number N to be printed. (Step S105). When the number "n"
does not exceed the total line number N, the above processing will
be repeated in the same manner for the line "n," and the driving
current correction data P will be memorized in the
driving-current-correction-data memory unit 40 for all the lines.
(Steps S101 through S105)
[0067] Next, again, n=1 is set in order to have the first line of
the total number of lines N targeted. (Step S106) Next, driving
current correction data P memorized in the
driving-current-correction-data memory unit 40 are fed to the
image-data correction calculation unit 44 (Step S107), and image
data are corrected in the image-data correction calculation unit
44. (Step S108) Next, corrected image data are fed to the LED print
head 7 (Step S109), and the LED elements are lighted in accordance
with the corrected image data. (Step S1110) Then, in order to have
the next line "n" targeted, an increment of +1 is supplied to the
number "n" (Step S111), checking to ensure that the number "n" does
not exceed the total line number N to be printed. (Step S112) When
the number "n" does not exceed the total line number N, the above
processing will be repeated in the same manner for the line "n."
(Steps S 107 through S112)
[0068] Subsequently, a third embodiment of the present invention
will be described with reference to FIGS. 9 and 10. FIG. 9 is a
block diagram showing the construction of an LED array control unit
in an image forming apparatus according to the third embodiment.
FIG. 10 is a flow chart showing a procedure for lighting control of
LED elements in the image forming apparatus. In FIG. 9, parts
having the same names as those in the figures of FIGS. 1 through 5
and FIG. 7 are denoted by the same reference numerals, and
explanation will be omitted when repeated. This will be the same
for a fourth through an eighth embodiments of the present invention
that will be described later.
[0069] The third embodiment is characterized in that the
selective-information-data feeding unit 60 according to the first
embodiment is changed to a detected-data feeding unit 70. In other
words, as shown in FIG. 9, the LED array control unit 34 is
provided with a detected-data feeding unit 70 externally. The
detected-data feeding unit 70 detects a change in the image forming
apparatus due to aging that gives an influence on a fluctuation of
image quality due to ageing, in other words, which means a change
in light quantity of the LED elements and in electrostatic charging
characteristic of the photoreceptor; and feeds the detected data to
the driving-current-correction-data calculation unit 39. The
detected-data feeding unit 70 has the following applied thereto,
including: a temperature sensor 71 which detects ambient
temperatures in the apparatus and feeds them as detected data; a
humidity sensor 72 which detects humidity in the apparatus and
feeds it as a detected datum; an output paper counter 73 which
detects the number of output paper having an image formed thereon
and feeds the total number of output paper and the number of paper
continuously output as detected data; a developing bias potential
sensor 74 which detects developing bias potentials and feeds them
as detected data; and a photoreceptor-surface potential sensor 75
which detects dark and light potentials of a surface of the
photoreceptor and feeds them as detected data; each of which is
installed at an appropriate location in an appropriate manner
inside the apparatus.
[0070] According to the third embodiment of the present invention,
the driving-current-correction-data calculation unit 39 is
connected to the characteristic-data memory unit 35 and the
detected-data feeding unit 70; reads out each of the characteristic
data memorized in the light-quantity-data memory unit 36, the
beam-data memory unit 37 and the resolution-data memory unit 38,
all of which are mounted in the characteristic-data memory unit 35;
receives detected data fed from the detected-data feeding unit 70;
calculates driving current correction data P for each of a
plurality of LED elements forming the LED array 31, based on the
characteristic data; and increases or decreases the driving current
correction data P in accordance with the detected data. Then, the
calculated and increased/decreased driving current correction data
P are fed to the image-data correction calculation unit 44.
[0071] Next, a procedure for lighting control of the LED elements
according to the third embodiment will be explained by referring to
FIG. 10. First of all, the same as the first embodiment, n=1 is set
to make the first line of the total number of lines N targeted.
(Step S201) Next, characteristic data of each of the LED elements
are read out from the characteristic-data memory unit 35, receiving
detected data fed from the detected-data feeding unit 70 (Step
S202), and driving current correction data P for each of the LED
elements are calculated and increased or decreased in the
driving-current-correction-data calculation unit 39. (Step S203)
Next, calculated and increased/decreased driving current correction
data P are fed to the image-data correction calculation unit 44.
(Step S204) Hereafter, a procedure including the steps S205 through
S209 corresponding to the steps S5 through S9 of the first
embodiment (See FIG. 6.) will be followed sequentially.
[0072] The same as the first embodiment, the third embodiment is so
constructed as to have driving current correction data P directly
fed to the image-data correction calculation unit 44 after the
driving current correction data P are calculated and
increased/decreased in the driving-current-correction-data
calculation unit 39. However, the same as the relationship between
the first and the second embodiments, as shown in FIG. 11, a fourth
embodiment of the present invention is separately provided with a
driving-current-correction-data memory unit 40 that memorizes
driving current correction data P calculated and
increased/decreased in the driving-current-correction-data
calculation unit 39, and has the driving-current-correction-data
memory unit 40 connected to the driving-current-correction-data
calculation unit 39 and to the image-data correction calculation
unit 44.
[0073] A procedure for lighting control of the LED elements
according to the fourth embodiment will be explained by referring
to FIG. 12. The same as the second embodiment, n-1 is set to make
the first line of the total number of lines N targeted. (Step S300)
Next, characteristic data of each of the LED elements are read out
from the characteristic-data memory unit 35, receiving detected
data fed from the detected-data feeding unit 70 (Step S301); and
driving current correction data P for each of the LED elements are
calculated and increased or decreased in the
driving-current-correction-data calculation unit 39. (Step S302)
Next, calculated and increased/decreased driving current correction
data P are memorized in the-driving-current-correction-data memory
unit 40. (Step 303) Then, after that, a procedure including the
steps S304 through S312 corresponding to the steps S104 through
S112 of the second embodiment (See FIG. 8.) will be followed
sequentially.
[0074] Next, a fifth embodiment of the present invention will be
described by referring to FIGS. 13 and 14. FIG. 13 is a block
diagram showing the construction of an LED array control unit of an
image forming apparatus according to the fifth embodiment. FIG. 14
is a flow chart showing a procedure for lighting control of the LED
elements in the image forming apparatus.
[0075] The fifth embodiment is characterized in that the
selective-information-data feeding unit 60 according to the first
embodiment is changed to a data-on-an-image-on-a-paper feeding unit
80. In other words, as shown in FIG. 13, an LED array control unit
34 is provided with the data-on-an-image-on-a-paper feeding unit 80
externally. The data-on-an-image-on-a-paper feeding unit 80 reads
an image formed on an output paper 14 by the image forming
apparatus, that is reflected in a fluctuation of image quality due
to ageing, in other words, a change in the light quantity of LED
elements, in the electrostatic charging characteristic of a
photoreceptor and in the charging characteristic of a toner; and
feeds data on an image formed on a paper mainly showing degree of
uneven density of the image to the driving-current-correction-data
calculation unit 39. The data-on-an-image-on-a-paper feeding unit
80 has an image sensor 81 applied thereto, which scans and reads an
image formed on an output paper. The image sensor 81 is so mounted
as to be in close proximity to the paper 14, facing to it, which is
immediately before passing through a fusing unit 17 (See FIG. 1.)
after transferring is finished.
[0076] According to the fifth embodiment of the present invention,
a driving-current-correction-data calculation unit 39 is connected
to a characteristic-data memory unit 35 and to a
data-of-an-image-on-a-paper feeding unit 80, reads out
characteristic data memorized in a characteristic-data memory unit
35, receives data on an image formed on a paper fed from the
data-of-an-image-on-a-paper feeding unit 80, calculates driving
current correction data P for each of a plurality of LED elements
forming an LED array 31 based on characteristic data, and increases
or decreases the driving current correction data P in accordance
with data of an image formed on a paper. Then, the calculated and
increased/decreased driving current correction data P are fed to
the image-data correction calculation unit 44.
[0077] Subsequently, a procedure for lighting control of the LED
elements according to the fifth embodiment will be explained by
referring to FIG. 14. First of all, the same as the first
embodiment, n-1 is set to make the first line of the total number
of lines N targeted. (Step S401) Next, characteristic data of each
of the LED elements are read out from the characteristic-data
memory unit 35, receiving data on an image formed on a paper fed
from the data-of-an-image-on-a-paper feeding unit 80 (Step S402);
and driving current correction data P for each of the LED elements
are calculated and increased or decreased in the
driving-current-correction-data calculation unit 39. (Step S403)
Then, the calculated and increased/decreased driving current
correction data P is fed to the data-of-an-image-on-a-paper
correction calculation unit 44. (Step S404) Hereafter, a procedure
including the steps S405 through S409 corresponding to the steps S5
through S9 of the first embodiment (See FIG. 6.) will be followed
sequentially.
[0078] The same as the first embodiment, the fifth embodiment is so
constructed as to have driving current correction data P directly
fed to the image-data correction calculation unit 44 after the
driving current correction data P are calculated and
increased/decreased in the driving-current-correction-data
calculation unit 39. However, according to a sixth embodiment of
the present invention, the same as the relationship between the
first and the second embodiments (corresponding to the relationship
between the third and the fourth embodiments), as shown in FIG. 15,
a driving-current-correction-data memory unit 40 is provided
separately, that memorizes driving current correction data P
calculated and increased/decreased in the
driving-current-correction-data calculation unit 39, and the
driving-current-correction-data memory unit 40 is connected to the
driving-current-correction-data calculation unit 39 and to the
image-data correction calculation unit 44.
[0079] A procedure for lighting control of the LED elements
according to the sixth embodiment will be explained by referring to
FIG. 16. First of all, the same as the second embodiment, n=1 is
set to make the first line of the total number of lines N targeted.
(Step S500) Next, characteristic data of each of the LED elements
are read out from the characteristic-data memory unit 35, receiving
data of an image formed on a paper fed from the
data-of-an-image-on-a-paper feeding unit 80 (Step S501), and
driving current correction data P for each of the LED elements are
calculated and increased or decreased in the
driving-current-correction-data calculation unit 39. (Step S502)
Next, calculated and increased/decreased driving current correction
data P are memorized in the driving-current-correction-data memory
unit 40. (S503). Then, after that, a procedure including the steps
S504 through S512 corresponding to the steps S104 through S112 of
the second embodiment (See FIG. 8.) will be followed
sequentially.
[0080] Next, a seventh embodiment of the present invention will be
described by referring to FIG. 17. FIG. 17 is a block diagram
showing the construction of an LED array control unit in an image
forming apparatus according to the seventh embodiment.
[0081] The seventh embodiment is characterized in that the
data-of-an-image-on-a-paper feeding unit 80 according to the fifth
embodiment is changed to a data-on-a-toner-image feeding unit 85.
In other words, as shown in FIG. 17, the LED array control unit 34
has a data-on-a-toner-image feeding unit 85 provided externally.
The data-on-a-toner-image feeding unit 85 reads out a toner image
formed on an image-carrying substance (e.g. a photoreceptor 5) by
the image forming apparatus, reflected in a fluctuation of image
quality due to ageing, and feeds toner image data mainly
representing the degree of uneven density of the toner image to the
driving-current-correction-data calculation unit 39. The
data-on-a-toner-image feeding unit 85 has an image sensor 86
applied thereto that scans and reads out a toner image formed on an
image-carrying substance. The image sensor 86 is so mounted as to
be in close proximity to a photoreceptor 5, facing to it, between
each of developing units 4 and each of image transfer rollers 9
(See FIG. 1.) when the image-carrying substance is a photoreceptor
5.
[0082] According to the seventh embodiment, the
driving-current-correction-data calculation unit 39 is connected to
the characteristic-data memory unit 35 and to the
data-on-a-toner-image feeding unit 85, reads out characteristic
data memorized in the characteristic-data memory unit 35, receives
data on a toner image fed from the data-on-a-toner-image feeding
unit 85, calculates operating current correction data P for each of
a plurality of the LED elements forming an LED array 31 based on
the characteristic data, and increases or decreases the driving
current correction data P in accordance with the data on a toner
image in accordance with a predetermined calculation formula. Then,
the calculated and increased/decreased driving current correction
data P are fed to the image-data correction calculation unit 44. A
procedure for lighting control of the LED elements is satisfied by
receiving data on a toner image in place of data on an image on a
paper in the step S402 in FIG. 14.
[0083] The same as the fifth embodiment, the seventh embodiment of
the present invention is so constructed as to have driving current
correction data P directly fed to an image-data correction
calculation unit 44 after the driving current correction data P are
calculated and increased/decreased in the
driving-current-correction-data calculation unit 39. However,
according to an eight embodiment of the present invention, the same
as the relationship between the fifth and the sixth embodiments, as
shown in FIG. 18, a driving-current-correction-data memory unit 40
is provided separately, that memorizes the driving current
correction data P calculated and increased/decreased in the
driving-current-correction-data calculation unit 39, and the
driving-current-correction-data memory unit 40 is connected to the
driving-current-correction-data calculation unit 39 and to the
image-data correction calculation unit 44. According to the eight
embodiment, a procedure for lighting control of the LED elements is
satisfied by receiving data on a toner image in place of data on an
image formed on a paper in the step S501 in FIG. 16.
[0084] FIGS. 19A and 19B show the relationship between the exposure
intensity of the LED elements and the beam diameter in the
development threshold value. Here, FIG. 19A shows the relationship
between the exposure intensity of the LED elements and the beam
diameter in the development threshold value before image data are
corrected, while FIG. 19B shows the relationship between the
exposure intensity of the LED elements and the beam diameter in the
development threshold value after image data are corrected. As
shown in FIG. 19A, either in a high-level density part or in a
low-level density part, an LED element "a" and an LED element "b"
have approximately the same quantity of light emitted (the peak
area in the figure), but the beam diameter differs. (Generally, the
beam diameter is specified within the range of 13.5% of the peak
light quantity.) In other words, in either high-level or low-level
density part, the LDE element "b" has a larger beam diameter than
the LED "a." (D.sub.b>D.sub.a and d.sub.b>d.sub.a)
[0085] However, as shown in FIG. 19A, in the high-level density
part, the dot diameter S.sub.b in the development threshold value
of the LED element "b" is larger than the dot diameter S.sub.a of
the LED element "a." On the other hand, in the low-level density
part, contrary to the high-level density part, the dot diameter sa
in the development threshold value of the LED element "a" is larger
than the dot diameter S.sub.b of the LED element "b." In other
words, the size relationship of the dot diameters in the
development threshold value between the LED element "a" and the LED
element "b" does not depend on the size relationship of the above
beam diameters, but depends on indication density of the LED
elements. Therefore, under these circumstances, in the high-level
density part, the LED element "b" having a larger dot diameter in
the development threshold value has larger dots of a latent image,
while in the low-level density part, the LED element "a" having a
larger dot diameter in the development threshold value has larger
dots of a latent image, and as a result, both will be expressed in
dark in images.
[0086] Therefore, beam diameters of the LED element "a", and the
LED element "b" in each level of indication density parts are
memorized as characteristic data in advance, and correction data
are made for driving current by using characteristic data
concerning the beam diameters, thus canceling the difference in
contrast of the indication density of the LED element "a" and the
LED element "b" in each level of indication density parts.
[0087] In other words, as shown in FIG. 19B, driving current
correction data are made by using characteristic data concerning
the beam diameters in such a manner as, in the high-level density
part, driving current of the LED element "b" having a large beam
diameter (and a large dot diameter) is decreased and driving
current of the LED element "a" having a small beam diameter (and a
small dot diameter) is increased; while driving current correction
data are made by using characteristic data concerning the beam
diameters in such a manner as, in the low-level density part,
driving current of the LED element "b" having a large beam diameter
(but a small dot diameter) is increased and driving current of the
LED element "a" having a small diameter (but a large dot diameter)
is decreased. By making driving current correction data in the
above-mentioned ways, the dot diameters of the LED element "a" and
the LED element "b" in the development threshold value in each
level of indication density parts will be the same. As a result, it
is possible to cancel the difference in contrast of indication
density of the LED element "a" and the LED element "b" in each
level of the indication density parts.
[0088] FIGS. 19A and 19B shows a case where driving current
correction data are made by using beam diameters as characteristic
data of the LED elements. However, as mentioned above, it is also
possible to make driving current correction data by using as
characteristic data, light quantity data of each of the LED
elements, data on beam area and data showing resolution such as MTF
data and the like, individually or combining a plurality of data
thereof.
[0089] As a result, according to each of the above-mentioned
embodiments, each individual LED element forming an LED array 31
has a characteristic-data memory unit 35 mounted thereon for
memorizing a plurality of characteristic data that are measured in
advance and that are contributing factors to occurrence of uneven
density of images, and also has the following mounted thereon,
including: a selective-information-data feeding unit 60 which feeds
information data corresponding to selective information that is
selected from the inherent selective information and is affecting
image quality; a detected-data feeding unit 70 that feeds detected
data on a change due to ageing affecting a fluctuation of image
quality due to ageing; a data-on-a-image-on-a-paper feeding unit 80
that reads out an image formed on an output paper 14 reflected in a
fluctuation of image quality due to ageing and feeds data of an
image formed on a paper thereof; and a data-on-a-toner-image
feeding unit 85 that reads a toner image formed on an
image-carrying substance such as a photoreceptor 5 and the like and
feeds data on a toner image thereof.
[0090] The driving-current-correction-data calculation unit 39
reads out characteristic data memorized in the characteristic-data
memory unit 35 and receives information data fed from the
selective-information-data feeding unit 60, detected data fed from
the detected-data feeding unit 70, or data on an image formed on a
paper fed from the data-on-an-image-on-a-paper feeding unit 80 and
data on a toner image fed from the data-on-a-toner-image feeding
unit 85. Then, the driving-current-correction-data calculation unit
39 calculates driving current correction data P concerning each
individual LED element forming the LED array 31 based on
characteristic data and information data, calculates driving
current correction data P concerning each individual LED element
based on characteristic data, and increases or decreases the
driving current correction data P in accordance with the detected
data or data on an image formed on a paper or data on a toner
image. The driving current correction data calculation unit 39 is
so constructed as to have driving current based on the driving
current correction data P flow to the LED elements forming the LED
array 31. As a result, the difference in contrast of indication
density among the LED elements can be cancelled with a good
precision, restraining uneven density of images. Consequently, it
is possible to reduce occurrence of vertical streaks on images
efficiently.
[0091] Additionally, according to each of the above-mentioned
embodiments, the characteristic data memory unit 35 is so
constructed as to have a transferable PROM used therein. Therefore,
even when a change occurs in properties of each individual LED
element, it is possible to transfer characteristic data for each of
the LED elements smoothly. As a result, since it is possible to
calculate driving current correction data for each of the LED
elements with a good precision in calculating driving current
correction data P, it is possible to correct image data with high
precision.
[0092] According to each of the above-mentioned embodiments, the
photoreceptor is shaped in a drum. However, the photoreceptor is
not limited to being drum-shaped, but for example, a belt-shaped
photoreceptor may be used. Moreover, an image-carrying substance is
not limited to the photoreceptor 5. For example, an image forming
apparatus adopting a two-stage image-transferring method, wherein a
toner image formed on the photoreceptor 5 is once transferred to a
transport belt 8 in each of an image forming apparatus according to
the above embodiments and then the transferred toner image is
re-transferred to a paper 14, may have the transport belt 8 be an
image-carrying substance.
[0093] Also, according to each of the above-mentioned embodiments,
an image forming apparatus is so constructed as to obtain color
images in accordance with images of toners in black, yellow, cyan
and magenta. The present invention may be applicable to a color
image forming apparatus employing more than two colors of toners
having different colors from each other.
[0094] While there have been described herein what are to be
considered preferred embodiments of the present invention, various
decorations and deformations to the present invention are possible
to be practiced, provided all such modifications fall in the spirit
and scope of invention.
* * * * *